My invention relates to the casting of molten metal in an open ended mold cavity, and in particular, to the peripheral confinement of the molten metal in the cavity during the casting of it into an end product.
Present day open ended mold cavities have an entry end, a discharge end opening, an axis extending between the discharge end opening and the entry end of the cavity, and a wall circumposed about the axis of the cavity between the discharge end opening and the entry end thereof to confine the molten metal to the cavity during the passage of the metal through the cavity. When a casting operation is to be carried out, a starter block is telescopically engaged in the discharge end opening of the cavity. The block is reciprocable along the axis of the cavity, but initially, it is stationed in the opening while a body of molten startup material is interposed in the cavity between the starter block and a first cross sectional plane of the cavity extending relatively transverse the axis thereof. Then, while the starter block is reciprocated relatively outwardly from the cavity along the axis thereof, and the body of startup material is reciprocated in tandem with the starter block through a series of second cross sectional planes of the cavity extending relatively transverse the axis thereof, layers of molten metal having lesser cross sectional areas in planes transverse the axis of the cavity than the cross sectional area defined by the wall of the cavity in the first cross sectional plane thereof, are successively superimposed on the body of startup material adjacent the first cross sectional plane of the cavity. Because of their lesser cross sectional areas, each of the respective layers has inherent splaying forces therein acting to distend the layer relatively peripherally outwardly from the axis of the cavity adjacent the first cross sectional plane thereof. It so distends until the layer is intercepted by the wall of the cavity where, due to the fact that the wall is at right angles to the first cross sectional plane of the cavity, the layer is forced to undergo a sharp right angular turn into the series of second cross sectional planes of the cavity, and to undertake a course through them parallel to that of the wall, i.e., perpendicular to the plane. Meanwhile, on contact with the wall, the layer begins to experience thermal contraction forces, and in time, the thermal contraction forces effectively counterbalance the splaying forces and a condition of xe2x80x9csolidusxe2x80x9d occurs in one of the second cross sectional planes. Thereafter, as an integral part of what is now a newly formed body of metal, the layer proceeds to shrink away from the wall as it completes its passage through the cavity in the body of metal.
Between the first cross sectional plane of the cavity, and the one second cross sectional plane thereof wherein xe2x80x9csolidusxe2x80x9d occurs, the layer is forced into close contact with the wall of the cavity, and this contact produces friction which operates counter to the movement of the layer and tends to tear at the outer peripheral surface of it, even to the extent of tending to separate it from the layers adjoining it. Therefore, practitioners in the art have long attempted to find ways either to lubricate the interface between the respective layers and the wall, or to separate one from the other at the interface therebetween. They have also sought ways to shorten the width of the band of contact between the respective layers and the wall. Their efforts have produced various strategies including that disclosed in U.S. Pat. No. 4,598,763 and that disclosed in U.S. Pat. No. 5,582,230. In U.S. Pat. No. 4,598,763, an oil encompassed sleeve of pressurized gas is interposed between the wall and the layers to separate one from the other. In U.S. Pat. No. 5,582,230, a liquid coolant spray is developed around the body of metal and then driven onto the body in such a way as to shorten the width of the band of contact. Their efforts have also produced a broad variety of lubricants; and while their combined efforts have met with some success in lubricating and/or separating the layers from the wall and vice versa, they have also produced a new and different kind of problem relating to the lubricants themselves. There is a high degree of heat exchanged across the interface between the layers and the wall, and the intense heat may decompose a lubricant. The products of its decomposition often react with the ambient air in the interface to form particles of metal oxide and the like which become xe2x80x9crippersxe2x80x9d at the interface that in turn produce so-called xe2x80x9czippersxe2x80x9d along the axial dimension of any product produced in this way. The intense heat may even cause a lubricant to combust, creating in turn a hot metal to cold surface condition wherein the frictional forces are then largely unrelieved by any lubricant whatsoever.
My invention departs entirely from the prior art strategies for separating or lubricating the layers from the wall at the interface therebetween, and from the prior art strategies for shortening the band of contact between the two. Instead, my invention eliminates the xe2x80x9cconfrontationxe2x80x9d between the layers and wall that gave rise to the problems requiring these prior art strategies, and in their place, substitutes a whole new strategy for confining the relatively peripherally outward distention of the respective layers in the cavity during the passage of the molten metal therethrough.
According to my invention, I now arrange baffling means about the axis of the cavity in the means for confining the outer periphery of the molten metal to the cavity during the passage of the metal through the cavity, and while confining the relatively peripheral outward distention of the respective layers of molten metal to first and second cross sectional areas of the cavity in the first and second cross sectional planes thereof, respectively, I operate the baffling means to achieve certain effects at the circumferential outlines of the respective areas. Firstly, I operate the baffling means at the circumferential outline of the first cross sectional area so that the baffling effect thereof directs the respective layers into the series of second cross sectional planes of the cavity at relatively peripherally outwardly inclined angles to the axis thereof. And secondly, while the splaying forces in the respective layers exceed the thermal contraction forces inherently arising therein, I operate the baffling means at the circumferential outlines of the second cross sectional areas so that the baffling effect thereof enables the respective second cross sectional areas to assume progressively peripherally outwardly greater cross sectional dimensions in the second cross sectional planes corresponding thereto while the thermal contraction forces counterbalance the splaying forces and enable the respective layers to freeform a body of metal in one of the second cross sectional planes of the cavity. In this way, I no longer confront the layers with a wall or some other peripheral confinement means, but like a parent teaching a child to walk by extending an outstretched arm on which the child can lean while the parent gradually backs away from the child, so too I give the layers the same kind of passive support at the outer peripheries thereof, and xe2x80x9cencouragexe2x80x9d them to aggregate on their own, and to form a coherent skin of their own choosing, rather than accepting one imposed on them by a surrounding wall or the like. Also, as fast as the thermal contraction forces can take over from the effects of my baffling means, I withdraw the effects so that contact between the layers and any restraining medium is virtually eliminated. This means that I no longer need to lubricate or buffer the interface between the layers and a peripheral confinement means, but it does not preclude my continuing to use a lubricating or buffering medium in the interface. In fact, in many of the presently preferred embodiments of my invention, I interpose a sleeve of pressurized gas between the baffling means and the circumferential outlines of the respective layers in the first and second cross sectional planes of the cavity. I also commonly interpose an annulus of oil between the baffling means and those outlines, and in certain embodiments I interpose an oil encompassed sleeve of pressurized gas between the two, as in U.S. Pat. No. 4,598,763. I commonly also discharge the pressurized gas into the cavity through the baffling means, and I may also discharge the oil into the cavity through the baffling means. Often, I discharge them into the cavity simultaneously.
In many of the presently preferred embodiments of my invention, I also arrange heat extraction means about the axis of the cavity, and I operate the heat extraction means to extract heat from the angularly successive part annular portions of the layers arrayed about the circumferences thereof. In some of these embodiments, I also operate the baffling means to confer the circumferential outlines on the respective first and second cross sectional areas of the layers in the cavity. And in certain of them, I open up a whole new world of possibilities for open ended mold casting by arranging about the axis of the cavity, axis orientation control means for controlling the orientation of the axis to a vertical line, heat extraction control means for controlling the rate at which heat is extracted by the heat extraction means from the respective angularly successive part annular portions of the layers, first circumferential outline control means for controlling the circumferential outline conferred on the first cross sectional area by the baffling means, and second circumferential outline control means for controlling the circumferential outlines conferred on the respective second cross sectional areas by the baffling means, and operating the respective axis orientation control means, heat control means, and first and second circumferential outline control means in conjunction with the baffling means to confer any predetermined circumferential outline I may choose on the cross sectional area assumed by the body of metal in the one second cross sectional plane of the cavity.
At that plane, before major shrinkage occurs, the circumferential outline I confer on the body of metal will be larger than the circumferential outline I had conferred on the first cross sectional area with the baffling means. But I can easily account for that in the design of each mold, and knowing that, I may operate the first circumferential outline control means so as to cause the baffling means to confer a first circumferential outline on the first cross sectional area, and operate the axis orientation control means, the heat control means, and the second circumferential outline control means, in conjunction with the baffling means, to confer on the cross sectional area of the body of metal in the one second cross sectional plane of the cavity, a predetermined circumferential outline which is larger than but corresponds to the first circumferential outline conferred on the first cross sectional area by the baffling means. Or I may operate the axis orientation control means, the heat control means and the second circumferential outline control means, in conjunction with the baffling means, to confer on the cross sectional area of the body of metal in the one second cross sectional plane of the cavity, a predetermined circumferential outline which is larger than and differs from the first circumferential outline conferred on the first cross sectional area by the baffling means. To illustrate, there are times, such as when the first circumferential outline is an asymmetrical noncircular circumferential outline, that it generates a variance between the differentials existing between the respective splaying forces and thermal contraction forces inherent in angularly successive part annular portions of the layers that are mutually opposed to one another across the cavity in second cross sectional planes thereof, and I may operate the axis orientation control means, the heat control means, and the second circumferential outline control means, in conjunction with the baffling means, to neutralize that variance in third cross sectional planes of the cavity extending parallel to the axis thereof between the respective mutually opposing angularly successive part annular portions of the layers. At other times, such as when the first circumferential outline is a circular circumferential outline, the first circumferential outline may be relatively devoid of a variance between the differentials existing between the respective splaying forces and thermal contraction forces inherent in portions that are mutually opposed to one another across the cavity in the second cross sectional planes thereof, and I may operate the respective axis orientation control means, heat control means, and second circumferential outline control means, in conjunction with the baffling means, to create a variance between the aforesaid differentials in third cross sectional planes of the cavity extending parallel to the axis thereof between mutually opposing angularly successive part annular portions of the layers. For example, the first circumferential outline I confer on the first cross sectional area, may be a circular circumferential outline, and I may operate the axis orientation control means, the heat control means, and the second circumferential outline control means, in conjunction with the baffling means, to confer a symmetrical noncircular circumferential outline on the cross sectional area of the body of metal in the one second cross sectional plane of the cavity, such as an oval or oblate circumferential outline.
In one special case, I operate the first circumferential outline control means to cause the baffling means to confer a circular circumferential outline on the first cross sectional area, I operate the axis orientation control means to orient the axis of the cavity at an angle to a vertical line, such as at a horizontal, and I operate the heat control means and the second circumferential outline control means in conjunction with the baffling means, to confer a circumferential outline on the cross sectional area assumed by the body of metal in the one second cross sectional plane of the cavity, which is simply a predetermined circular outline that is larger in diameter than the first circumferential outline.
The cross sectional dimensions of the body of metal are also within the realm of control that I may exercise in practicing my invention. In one special group of embodiments, I arrange first cross sectional area control means about the axis of the cavity for controlling the cross sectional dimensions conferred on the cross sectional area assumed by the body of metal in the one second cross sectional plane of the cavity, and I operate the first cross sectional area control means in conjunction with the baffling means to confer predetermined cross sectional dimensions on the cross sectional area assumed by the body of metal between a first pair of mutually opposing sides of the cavity in the one second cross sectional plane thereof. Furthermore, in certain embodiments of the group, I add circumferential outline control to cross sectional dimensional control, by arranging circumferential outline control means about the axis of the cavity for controlling the circumferential outlines conferred on the respective first and second cross sectional areas by the baffling means and operating the circumferential outline control means in conjunction with the baffling means to confer a predetermined circumferential outline on the cross sectional area assumed by the body of metal between the first pair of sides of the cavity. And in embodiments which might be characterized as providing an adjustable mold, I arrange second cross sectional area control means about the axis of the cavity for controlling the cross sectional dimensions conferred on the cross sectional area assumed by the body of metal in the one second cross sectional plane of the cavity, and I operate the second cross sectional area control means in conjunction with the baffling means to confer predetermined cross sectional dimensions on the cross sectional area assumed by the body of metal between a second pair of mutually opposing sides of the cavity disposed at right angles to the first pair of sides in the one cross sectional plane of the cavity. For example, in certain embodiments for producing ingot, and in particular, so-called xe2x80x9crolling ingot,xe2x80x9d I operate the second cross sectional area control means to vary the lengthwise dimensions of a generally rectangular cross sectional area assumed by the body of metal, I operate the circumferential outline control means to confer a relatively bulbous circumferential outline on the midsection extending between the relatively longer sides of the rectangular cross sectional area, and I operate the first cross sectional area control means to maintain a predetermined cross sectional dimension between the longer sides of the rectangular cross sectional area when the lengthwise dimensions of the area are varied. That is, I do something which the prior art was incapable of doing with an adjustable mold: I maintain a predetermined cross sectional dimension between the longer sides of the area being cast while varying the lengthwise dimensions of that area in the mold.
I may control the cross sectional dimensions conferred on the cross sectional area assumed by the body of metal in one of several ways. I may shift the baffling means and the first and second cross sectional planes of the cavity in relation to one another along the axis of the cavity, such as by varying the volume of molten metal superimposed on the body of startup material in the respective layers of molten metal, or by rotating the baffling means about an axis of orientation transverse the axis of the cavity. Or in the context of an adjustable mold, I may divide the baffling means into pairs thereof, arrange the respective pairs of baffling means about the axis of the cavity on pairs of mutually opposing sides thereof, and shift the respective pairs of baffling means in relation to one another crosswise the axis of the cavity to control the cross sectional dimensions conferred on the cross sectional area assumed by the body of metal. For example, I may reciprocate one of the pairs of baffling means in relation to one another crosswise the axis of the cavity to shift the pairs thereof in relation to one another.
On occasion, I may even divide the baffling means into a pair thereof, arrange the pair of baffling means about the axis of the cavity in axial succession to one another, and shift the pair of baffling means in relation to one another axially of the cavity to control the cross sectional dimensions conferred on the cross sectional area assumed by the body of metal. In some embodiments of my invention, for example, I invert the pair of baffling means axially of the cavity to shift one in relation to the other. And in certain of them, I confer the same cross sectional dimensions on the cross sectional area assumed by the body of metal with the respective baffling means. That is, I employ the feature simply as a way to replace one baffling means with another, say when one of them is in need of servicing or replacement.
In a group of embodiments which I shall illustrate in the drawings accompanying my Application, I also operate the baffling means to confine the relatively peripheral outward distention of the respective layers to the first and second cross sectional areas thereof. For example, rather than employing electromagnetic baffling means, or sets of air knives, or some other such baffling means, I form a series of annular surfaces about the axis of the cavity on the baffling means, and I orient the respective surfaces to the axis of the cavity so as to confine the relatively peripheral outward distention of the layers to the first and second cross sectional areas of the cavity while generating the aforedescribed baffling effects at the circumferential outlines thereof. In one group of these embodiments, I arrange the respective annular surfaces in axial succession to one another, I stagger the surfaces relatively peripherally outwardly from one another in the respective first and second cross sectional planes of the cavity, and I orient the surfaces along relatively peripherally outwardly inclined angles to the axis of the cavity so that the baffling effects thereof operate as described. To control the circumferential outline conferred on the first cross sectional area by the baffling means, I vary the circumferential outline circumscribed by the annular surface in the first cross sectional plane of the cavity. To control the circumferential outlines conferred on the second cross sectional areas by the baffling means, I vary the circumferential outlines circumscribed by the annular surfaces in the second cross sectional planes of the cavity. And in one subgroup, I vary in relation to one another, the angles at which angularly successive part annular portions of the surfaces are oriented to the axis of the cavity, so as to vary in this way the circumferential outlines circumscribed by the annular surfaces in the second cross sectional planes of the cavity. And where necessary, I also vary in relation to one another, the angles at which angularly successive part annular portions of the surfaces are oriented to the axis of the cavity on mutually opposing sides of the cavity, to neutralize a variance between the differentials existing between the respective splaying forces and thermal contraction forces in the angularly successive part annular portions of the layers which are disposed opposite the respective part annular portions of the surfaces on the mutually opposing sides of the cavity. Or to create a different outline from that of the first cross sectional area, I vary in relation to one another, the angles at which angularly successive part annular portions of the surfaces are oriented to the axis of the cavity on mutually opposing sides of the cavity, to create a variance between the differentials existing between the respective splaying forces and thermal contraction forces in the angularly successive port annular portions of the layers which are disposed opposite the respective part annular portions of the surfaces on the mutually opposing sides of the cavity.
Sometimes, I even interconnect the annular surfaces with one another axially of the cavity to form an annular skirt. In fact, I may even form the skirt on the peripheral confinement means. And where I circumpose an annular wall about the axis of the cavity as the peripheral confinement means, I often form the skirt about the inner periphery of the wall between the first cross sectional plane of the cavity and the discharge end opening thereof.
Where I form a portion of the wall with a graphite casting ring, I usually form the skirt about the inner periphery of the ring.
I may give the skirt a rectilinear flare about the inner periphery thereof in any of the foregoing embodiments, or I may give it a curvilinear flare about the inner periphery thereof.
For heat extraction, I commonly discharge liquid coolant onto the body of metal at the other side of the one second cross sectional plane of the cavity from the first cross sectional plane thereof, and I control the volume of liquid coolant discharged onto the respective angularly successive part annular portions of the body of metal to control the rate at which heat is extracted from the respective part annular portions of the body of metal in third cross sectional planes of the cavity extending parallel to the axis thereof. Moreover, I commonly also vary the volume of liquid coolant discharged onto the respective part annular portions of the body of metal disposed at mutually opposing sides of the cavity, to balance the thermal stresses arising between the respective mutually opposing part annular portions in third cross sectional planes of the cavity extending therebetween. Preferably, I also discharge the liquid coolant onto the body of metal between planes transverse the axis of the cavity and coinciding with the bottom and rim of the trough-shaped model formed by the successively convergent isotherms of the body of metal.
I may discharge the liquid coolant onto the body of metal from an annulus formed about the axis of the cavity between the one second cross sectional plane of the cavity and the discharge end opening thereof, or I may discharge the liquid coolant onto the body of metal from an annulus formed about the axis of the cavity on the other side of the discharge end opening of the cavity from the one second cross sectional plane thereof. Preferably, I discharge the liquid coolant from a series of holes arranged about the axis of the cavity and divided into rows of holes in which the respective holes thereof are staggered in relation to one another from row to row, as in U.S. Pat. No. 5,582,230.
In many of the presently preferred embodiments of my invention, I actually arrange the series of holes in the cavity at the inner periphery thereof; but in others, I arrange the series of holes relatively outside of the cavity adjacent the discharge end opening thereof.
At times, I also operate the baffling means to generate a reentrant baffling effect in cross sectional planes of the cavity extending transverse the axis thereof between the one second cross sectional plane of the cavity and the discharge end opening thereof, to induce xe2x80x9crebleedxe2x80x9d to reenter the body of metal.
At times, I also superimpose sufficient layers of the molten metal on the body of startup material to elongate the body of metal axially of the cavity. When I do so, I may also subdivide the elongated body of metal into successive longitudinal sections thereof, and I may in addition, post-treat the respective longitudinal sections, such as by post-forging them.